think in java中Interrupting2.java示例中关于锁的问题？

问题描述

问 题

书上说如果试图从第二个任务中调用f()，那么将总会音Mutex不可获得而被阻塞，我的疑问是这里构造器中获取lock的任务和调用lock的任务不是同一个任务吗？为什么Blocked2中调用blocked.f()的时候阻塞？下面是代码：

class BlockedMutex {
  private Lock lock = new ReentrantLock();
  public BlockedMutex() {
    // Acquire it right away, to demonstrate interruption
    // of a task blocked on a ReentrantLock:
    lock.lock();
  }
  public void f() {
    try {
      // This will never be available to a second task
      lock.lockInterruptibly(); // Special call
      print("lock acquired in f()");
    } catch(InterruptedException e) {
      print("Interrupted from lock acquisition in f()");
    }
  }
}

class Blocked2 implements Runnable {
  BlockedMutex blocked = new BlockedMutex();
  public void run() {
    print("Waiting for f() in BlockedMutex");
    blocked.f();
    print("Broken out of blocked call");
  }
}

public class Interrupting2 {
  public static void main(String[] args) throws Exception {
    Thread t = new Thread(new Blocked2());
    t.start();
    TimeUnit.SECONDS.sleep(1);
    System.out.println("Issuing t.interrupt()");
    t.interrupt();
  }
} /* Output:
Waiting for f() in BlockedMutex
Issuing t.interrupt()
Interrupted from lock acquisition in f()
Broken out of blocked call
*///:~

解决方案

1. BlockedMutex的构造方法调用了Lock.lock()以后没有Release()

2. 调用lock.lockInterruptibly()和Lock.lock()是在两个线程中

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